1. Field of the Invention
The present invention broadly relates to missile fin control and, more particularly, is concerned with an actuator of minimum height using a single large diameter bearing having both radial and thrust capacity to support a fin shaft and thereby permitting better aerodynamic shaping of the missile body.
2. Description of the Prior Art
In conventional practice, missile control fins are commonly positioned by actuators mounted completely within the missile aft body. A fin is usually attached to an actuator by means of a circular shaft through which rotational torques and speeds, required for missile control, are achieved. In general, a high degree of torsional and bending stiffness is required. Actuators may be electrically, pneumatically, or hydraulically powered.
One conventional actuator shown in a group of four thereof in FIG. 1 and in dashed line form in FIG. 3 has two bearings spaced apart, one above the other, at distance "d" along the fin shaft to allow the shaft to rotate freely and react loads R.sub.1 and R.sub.2 imposed by the fin shaft due to aerodynamic loads on the fin. In conventional actuators. distance d is a minimum bearing spacing compatible with maximum allowable bearing loads. These bearing loads are transferred to the actuator housing and finally reacted to the missile body to accomplish the desired missile attitude.
One shortcoming of this conventional actuator design is that it can result in excessive actuator height, designated as "h" in FIG. 1, extending beyond the missile. Thus, a problem is presented in that additional aerodynamic fairings are required to minimize the additional drag which is otherwise produced due to the excessive actuator height. A second shortcoming is that root torsional and bending stiffness to meet flutter requirements is limited by the diameter of the actuator fin shaft. Larger diameter fin shafts may be used to increase torsional and bending stiffness but result in more exposed areas, again resulting in greater drag penalty.
As a consequence, a need exists for improvement in actuator construction to reduce its height or extension beyond the missile body and thereby eliminate costly corrective measures required to be taken as a result thereof. Such need is met by a fin extension of rectangular cross-section, with wedged or rounded front and back faces to reduce drag, and terminating as a large diameter support of the inner race of a large diameter bearing which is capable of simultaneously reacting radial and reversing thrust loads.